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post #1 of 47 Old 03-06-2013, 08:53 PM Thread Starter
hearld5000
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Hemi Performance / MPG

I know there are a lot of threads regarding WK Hemi performance and MPG, but I haven't found one thats fairly conclusive?

I bought an 06' Hemi with 40k miles on it in November but I'm not terribly impressed with the performance...All maintenance items had been replaced 10k miles ago so not too worried about plugs, etc. Thoughts?

Whats the best bang for the buck for performance?
Whats the best bang for the buck for highway MPG?

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post #2 of 47 Old 03-07-2013, 01:17 AM
anthonyribeca
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A light foot
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post #3 of 47 Old 03-07-2013, 04:59 AM
JeepWKHemi
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There isn't much. Drive it lightly, don't "open her up," etc... It's just the nature of the beast while driving during the Winter in cold locations. During the Winter here in Fargo, I average between 10 to 14 MPG depending on my driving. However, during the summer I am breaking the 20 MPG marker.

You weren't expecting to get 30 mpg outta a Hemi, were ya?

BTW, I love how those rims look on your WK! I'm considering a set of take-offs from the local dealership. Just not sure about the tire size, but you say there is no rubbing what so ever? Kinda hard to believe given the experiences that I have read about with that size.

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post #4 of 47 Old 03-07-2013, 05:50 AM
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post #5 of 47 Old 03-07-2013, 07:07 AM Thread Starter
hearld5000
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Quote:
Originally Posted by JeepWKHemi View Post
There isn't much. Drive it lightly, don't "open her up," etc... It's just the nature of the beast while driving during the Winter in cold locations. During the Winter here in Fargo, I average between 10 to 14 MPG depending on my driving. However, during the summer I am breaking the 20 MPG marker.

You weren't expecting to get 30 mpg outta a Hemi, were ya?

BTW, I love how those rims look on your WK! I'm considering a set of take-offs from the local dealership. Just not sure about the tire size, but you say there is no rubbing what so ever? Kinda hard to believe given the experiences that I have read about with that size.
I hope thats the case, only had it since November and I'm averaging 10-12 around town, pretty bad. Nope, wasn't expecting 30, don't have that big of an imagination ha.

Thanks, I haven't seen another WK with the new Rubicon wheels so kind of fun. I've been surprised too, haven't been able to get it to rub at all except after a run up the mountains and got a bunch of ice buildup. Its close though, watching the fronts as my buddy turned the wheels it probably gets within 1/3 - 1/2 inch of rubbing on the rear of the wheelwell plastic. Still not sure if I want to cut "the bolt", probably has a 1/4-1/3 inch of clearance.
There might be a little different offset from the older Rubicon wheels that helps too, not sure. Didn't need spacers to clear the calipers...although I've read the may only apply to 2007+.

Quote:
Originally Posted by kebkid View Post
Superchips
Is there a preferred model? Flashpaq, vivid, etc? Is there a tune difference between models?
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post #6 of 47 Old 03-07-2013, 07:18 AM
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I have the XK HEMI and love its performance.. My biggest gain was the DiabloInTune, I did a ton of research before buying a tuner.. The InTune has the ability to adjust "throttle boast" or basically the sensitivity of the throttle, eliminating that delay when hitting the throttle. The tuner also allows you to adjust tire size which will help correct mpg reading on EVIC. I also saw a rise in mpg, city I was getting 13.3 with the 91 tune and 18.2 highway, keep in mind Im lifted, full skids, heavy foot and a bigger Jeep. Also have a CAI, which does nothing on low end performance but did help a tad bit with fuel economy... Now that its winter and I have the MTRs I get 12.2 city and still 17-18 mpg highway depending on my foot.. One last thing, dont get a CAI intake if youre expecting huge performance gains, cause it wont, only under WOT high RPM is where you may see gains, but it allows the engine to breathe easier or less restrictive, plus it sounds cool... Best bang for buck, tuner hands down

05 LJRubi Currie 4" Springs, Savvy Fox shocks, MC trackbars, MC CA's single adj lower double uppers, 37x13.50 Cooper STT Pros on 17x9 ATX Ravine, MC Overlines front, Genright rear, Revolution 5.38s, Carolina Driveline driveshafts, MCAI
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post #7 of 47 Old 03-07-2013, 01:32 PM
90grandoneer
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What everyone else said, and a little more. Remember, you're hauling around over 5000 lbs. with you and a full tank of fuel. Aside from "sane" driving, reducing it's weight (take all unnecessary junk out), improving aerodynamics and volumetric efficiency (VE) are the easist way to improve economy. As said, the best bang for the buck to start with is probably a tuner. I have both the Superchips and Diablosport tuners, and each has its advantages. No matter what you use in town, you won't see big gains due to the weight of the vehicle, and stop and go driving. For economy, the Diablosport gives me about .50-1.5 mpg better (on the highway) than the Superchips, when using the same octane tunes. If you want to get rid of the crappy operation of the 545RFE transmission (which I do), the Superchips, with the ATT App. is the best. I use the Diablosport with the 93 tune on my Hemi LX and get 15-16 mpg in town and 27-30 mpg on the highway. I use the Superchips 91 tune on the Hemi WK and get 12-14 mpg in town, and mostly 21-23 mpg on the highway....only been below 20 twice in a year and a half. See the mods. (both are modded the same) I have in my signature....I have substantially improved the VE, and in the process gained ~75-100 horsepower. I've also improved the aerodynamics on the WK by lowering it, adding a modified SRT front bumper, and vortex generators in the back. Also remember that no single mod. will make tons of difference, but cumulatively every little bit helps. My biggest gains, respectively, were from the tubular headers and complete 3 in. low restriction exhaust, and the cam and kit. Cost of all this (~$4000 over 3 years) doesn't bother me, as I keep my vehicles basically forever.

06 GCO, Dk Khaki, QDII, Flshing Hi 3rd Bk Lt, MDS "ON" Lt, Airtab Vortex Gens, Debadged, Fumoto Drain Valve, BT Catch Can, Chopped EGR Tube, SRT8 CAI, AFE Air Filter, 6spd 545RFE, Sonnax Trans Line Press Booster, SC Tuner W/Adv Trans Tune App, DS and HP tuners, Transgo Shift Kit, ARH Long Tube Hdrs w/3 in Magnaflow/Xlerator AP Exh Sys, Bilsteins, SRT Springs/Sways, Cust Eng Cvr, SRT8 frt/rear bumpers, FRI Sidewinder Cam w/6* advance/6.1 valvetrain, SLP 25% UD Pulley, BBK true 90mm T-Body, SOS Ign Coils w/.060 spark plug gaps, TEA ported/milled heads w/new valve seats, SRT Reps with 265/45&295/40X20's. Also 05 Hemi LX modded exactly like WK and, SOLD Comp Cammed 06 300CSRT8 just replaced with 2021 Tesla Model S Plaid with 1020 hp and 1050 lb. ft. of torque.
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post #8 of 47 Old 03-08-2013, 06:17 AM
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I also have the performance transmission tune from Diablo intune which improved performance but it holds the gear longer which may negatively affect MPG... For the most part if I'm easy on it, there's quite the difference over stock..

05 LJRubi Currie 4" Springs, Savvy Fox shocks, MC trackbars, MC CA's single adj lower double uppers, 37x13.50 Cooper STT Pros on 17x9 ATX Ravine, MC Overlines front, Genright rear, Revolution 5.38s, Carolina Driveline driveshafts, MCAI
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post #9 of 47 Old 03-08-2013, 08:49 AM
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06JeeXKHEMI, I've been wondering about the in Intune?? Does it give you full up/down shift control of all forward gears, or just the 1-2 and 2-3 upshifts? Does it also give you full control over the torque management for all upshifts and WOT? I know my regular Diablosport only allows control of 1-2 and 2-3 upshifts, no downshifts, and no torque management. Just wondering if I needed to upgrade to the Intune?? Thanks for any info. you can provide. The DS web site isn't much help in this regard.

As a side note, do you know what the drag coeficient is for the XK? The stock WK is .41, the stock WK SRT-8 is .39, and my LX is .35. I would guess yours is probably in the neighborhood of ~.43-.44, stock. With the lift probably a little worse due to the added under chassis turbulence and bigger tires.

06 GCO, Dk Khaki, QDII, Flshing Hi 3rd Bk Lt, MDS "ON" Lt, Airtab Vortex Gens, Debadged, Fumoto Drain Valve, BT Catch Can, Chopped EGR Tube, SRT8 CAI, AFE Air Filter, 6spd 545RFE, Sonnax Trans Line Press Booster, SC Tuner W/Adv Trans Tune App, DS and HP tuners, Transgo Shift Kit, ARH Long Tube Hdrs w/3 in Magnaflow/Xlerator AP Exh Sys, Bilsteins, SRT Springs/Sways, Cust Eng Cvr, SRT8 frt/rear bumpers, FRI Sidewinder Cam w/6* advance/6.1 valvetrain, SLP 25% UD Pulley, BBK true 90mm T-Body, SOS Ign Coils w/.060 spark plug gaps, TEA ported/milled heads w/new valve seats, SRT Reps with 265/45&295/40X20's. Also 05 Hemi LX modded exactly like WK and, SOLD Comp Cammed 06 300CSRT8 just replaced with 2021 Tesla Model S Plaid with 1020 hp and 1050 lb. ft. of torque.
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post #10 of 47 Old 03-09-2013, 08:52 AM
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It only allows up shifts as you stated, 1-2, 2-3 by selecting the sensitivity of the throttle.. So I did on my 1-2 shift, if Im over 60% throttle its staying in 1st, and IIRC 40% on 2-3. Also adjusts redline in every gear, my 2nd gear under WOT I will hit 90mph just under 6k RPM.. Unfortunately there is no TQ management that I can see, however once I stop being lazy and get my headers done Im having a custom tune drawn up for me by diablotuna.. You can adjust certain things like advance/retard but I dont know enough about it to mess with it and WOT settings.. I went with the InTune cause of the adjustable parameters I wanted, like TB boast which when set correct practically eliminates that annoying delay, also was suggested by diablotuna for when he does my custom tune.. Its worth the extra money but if you were to upgrade I think they have one above that, Trinity, if I were to spend $$$ Id go to that..
I dont know the drag coeficient for the XK, I imagine more than you said, its boxier, heavier and lifted, but again what do I know about coefficient drag?!?!

05 LJRubi Currie 4" Springs, Savvy Fox shocks, MC trackbars, MC CA's single adj lower double uppers, 37x13.50 Cooper STT Pros on 17x9 ATX Ravine, MC Overlines front, Genright rear, Revolution 5.38s, Carolina Driveline driveshafts, MCAI
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post #11 of 47 Old 03-09-2013, 11:22 AM
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Guess the drag coefficient of the Commander is not as bad as I thought.....only .415. I thought for sure it would be higher because of like you said, it's kind of boxy. It's only .005 worse than the stock WK. http://www.simpson260.com/hosting/jeeps/06jeep.htm and http://www.xkjeeps.com/xk_specs.htm I do know that very little difference in Cd makes a fair difference in economy.

Thanks for the info. Your Intune appears to have the same exact features I have (using the latest CROM file) in the regular DS tuner. Their website says the Intune is the replacement for the one I have. Too bad it doesn't have full tranny control like the SC tuner, since I'd prefer to use it....it gives a little better fuel economy and performance.

06 GCO, Dk Khaki, QDII, Flshing Hi 3rd Bk Lt, MDS "ON" Lt, Airtab Vortex Gens, Debadged, Fumoto Drain Valve, BT Catch Can, Chopped EGR Tube, SRT8 CAI, AFE Air Filter, 6spd 545RFE, Sonnax Trans Line Press Booster, SC Tuner W/Adv Trans Tune App, DS and HP tuners, Transgo Shift Kit, ARH Long Tube Hdrs w/3 in Magnaflow/Xlerator AP Exh Sys, Bilsteins, SRT Springs/Sways, Cust Eng Cvr, SRT8 frt/rear bumpers, FRI Sidewinder Cam w/6* advance/6.1 valvetrain, SLP 25% UD Pulley, BBK true 90mm T-Body, SOS Ign Coils w/.060 spark plug gaps, TEA ported/milled heads w/new valve seats, SRT Reps with 265/45&295/40X20's. Also 05 Hemi LX modded exactly like WK and, SOLD Comp Cammed 06 300CSRT8 just replaced with 2021 Tesla Model S Plaid with 1020 hp and 1050 lb. ft. of torque.
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post #12 of 47 Old 03-09-2013, 05:00 PM
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Quote:
Originally Posted by 90grandoneer View Post
.... I do know that very little difference in Cd makes a fair difference in economy....
As a general rule, up to ~45mph, mpg's depend primarily on vehicle weight. Above 45 mph, they are primarily dependent on drag force. Drag force is diectly proportional to Cd (drag coefficient related to shape) and square of the velocity.

The final mpg's are also influenced by the drive train torque curve. The old-time religion says that minimum brake-specific fuel consumption (BSFC) usually occurs at the peak of the torque curve. That is no longer as fixed with all of the new engine computer controls. The 5.7L HEMI's have a fairly flat & unique curve. See below.

OK - no more engineering / physics *****... I'm making up Test #3 and the lecture on linear momentum / elastic collisions / inelastic collisions. Needed a break.
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HEMI Curve.jpg  

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post #13 of 47 Old 03-11-2013, 10:35 PM
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image-1626673022.jpg

Lifted on 265/75/17
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post #14 of 47 Old 03-11-2013, 11:12 PM
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Quote:
Originally Posted by anthonyribeca

Lifted on 265/75/17
That's nothing


image-4092394633.jpg


Definitely the diablosport intune. I use the fuel saver tune and the rest of the mods in my sig. I only get that if I set the cruise to 55 and don't go above 60. I can get 20-22 at 65.

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post #15 of 47 Old 03-12-2013, 03:56 AM
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Y'all must be coasting down a hill when you took those readings. :P

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